In high-temperature furnaces, such as furnaces used for semiconductor processing or heated chambers used for metal organic chemical vapor deposition (MOCVD), it is necessary to monitor the temperature closely adjacent to where the process is being conducted. Thermocouples are used to monitor temperature; however, because of the corrosive environments present in such heated furnaces or chambers, it is necessary to sheath the thermocouple in a protection tube. The protection tube must not only be formed of material which withstands the corrosive processing environment, but should have a high coefficient of thermal conductivity, whereby the sheathed thermocouple will be rapidly sensitive to temperature fluctuations. For semiconductor processing applications, the protection tube must be chemically inert and of suitable chemical purity in order not to contaminate the wafer during processing. One particularly suitable material for thermocouple protection tubes is chemical vapor deposition-produced silicon carbide (CVD-SiC) as taught, for example, in U.S. Pat. No. 5,315,092, the teachings of which are incorporated herein by reference.
Solid CVD-SiC protection tubes are known. Production of these involves a significant amount of machining. Furthermore, while the high coefficient of thermal conductivity promotes responsiveness, the high thermal conductivity also promotes equalization of temperature throughout the tube, i.e., the temperature of the tube body tends to be translated to the tip where the temperature is being measured.